1. Technical Field
The present invention relates to a method and apparatus for placing sensors downhole in a well to monitor relevant formation characteristics. Specifically, the sensors can be flowed into the formation in the cement, or other suitable material, used to case the well. Alternatively, the sensors can be physically bored into the formation with a device described herein.
2. Description of the Related Art
Understanding an oil-bearing formation requires accurate knowledge of many conditions, such as critical rock and formation parameters at various points in the zones or formations that the oil bearing formation encompasses. Fluid pressure in the formation, its temperature, the rock stress, formation orientation and flow rates are a few examples of measurements taken within the formation which are useful in reservoir analysis. Having these formation/rock measurements available external to the immediate wellbore in wells within a producing field would facilitate the determination of such formation parameters such as vertical and horizontal permeability, flow regimes outside the wellbores within the formations, relative permeability, water breakthrough condensate banking, and gas breakthrough. Determinations could also be made concerning formation depletion, injection program effectiveness, and the results of fracturing operations, including rock stresses and changes in formation orientation, during well operations.
In addition to understanding oil bearing formations, the condition of the material used to set casing in a well is of critical interest in monitoring the integrity of a well completion. While cement is commonly used to set casing, other materials such as resins and polymers could be used. So while the term cement is used in this description, it is meant to encompass other suitable materials that might be used now or in the future to set casing. Pressure, temperature and stress, are a few examples of measurements taken within the cement that might be useful in determining the condition of the cement in a well. Various types of transducers placed near the cement/wellbore interface could be used to monitor the condition of the rock or formations outside the wellbore. Having these formation/rock measurements available external to the immediate wellbore in wells within a producing field would facilitate the determination of such formation parameters such as vertical and horizontal permeability, flow regimes outside the wellbores within the formations, relative permeability, potential fines migration, water breakthrough, and gas breakthrough. Determinations could also be made concerning formation depletion, fines migration, injection program effectiveness, and the results of fracturing operations, including rock stresses and changes in formation orientation, during well operations.
Historically, reservoir analysis has been limited to the use of formation measurements taken within the wellbores. Measurements taken within the wellbore are heavily influenced by wellbore effects, and cannot be used to determine some reservoir parameters. Well conditions such as the integrity of the cement job over time, pressure behind the casing, or fluid movement behind the casing cannot be monitored using the wellbore measurements.
Therefore, it is desirable to have a method and system that may be used to passively monitor reservoir/formation parameters at all depths and orientations outside a wellbore as well as having a method and system to passively monitor cement integrity. It is further desirable to have a method and system to take these measurements without compromising the casing, cement or any other treatment outside or inside the casing.
The present invention provides a method and system that may be used to passively monitor cement integrity and reservoir/formation parameters near the wellbore at all depths and orientations outside a wellbore. These measurements may be taken without compromising the casing, cement or any other treatment outside or inside the casing. In addition, sensors may be deployed in many more locations because of the non-intrusive nature of reading the sensors once they are in place.
In one embodiment, different types (pressure, temperature, resistivity, rock property, formation property etc.) of sensors are xe2x80x9cpumpedxe2x80x9d into place by placing them into a suspension in the cement slurry at the time a well casing is being cemented. The sensors are either battery operated, or of a type where external excitation, (EMF, acoustic, RF etc.) may be applied to power and operate the sensor, which will send a signal conveying the desired information. The sensor may then be energized and interrogated using a separate piece of wellbore deployed equipment whenever it is desired to monitor cement or formation conditions. This wellbore deployed equipment could be, for example, a wireline tool. Having sensors placed in this way allows many different types of measurements to be taken from the downhole environment. Looking at readings taken at different locations will allow directional properties such as permeability to be examined. Sensors placed close to the wellbore can be used to monitor the well integrity by disclosing information about cement condition, casing wear/condition etc. Sensors placed closer to the cement/wellbore interface provide reservoir or rock property measurements, which may be used in reservoir analysis.
In another embodiment, the sensors are placed into the formation at or outside the wellbore and may be interrogated whenever it is desired to monitor well or formation conditions. One method of placing the sensors into the formation is to use technology similar to side bore coring tools which remove samples in a direction that is perpendicular to the wellbore. Another method involves placing the sensors into the gravel slurry used for gravel packing and frackpacking operations thus allowing the sensors to migrate into the formation with the fracpack.
There are many advantages of the proposed system. First, non-intrusive downhole measurements may be taken from numerous locations in the downhole environment. Next, the integrity of the cement job can be closely monitored for initial quality, and degradation with time. Further, many transducers may be placed into the well with relatively low deployment cost. Also, very accurate measurements can be taken because of transducer placement outside the wellbore. Also, very long service life of transducers is achieved because power is supplied by a wellbore device capable of supplying transducer excitation power. Finally, fluid movement and pressure behind the casing may be measured by comparing the many available downhole measurements.